Auto complete textbox is not working c#

AutoCompleteStringCollection namesCollection = new AutoCompleteStringCollection();
            SqlDataReader dReader;
            SqlConnection conn = new SqlConnection();
            conn.ConnectionString = "Data Source=" ";Initial Catalog=" ";User ID=" ";Password=" "";
            SqlCommand cmd = new SqlCommand();
            cmd.Connection = conn;
            cmd.CommandType = CommandType.Text;
            cmd.CommandText = "Select distinct UserName from Users order by UserName asc";
            conn.Open();
            dReader = cmd.ExecuteReader();
            if (dReader.HasRows == true)
            {
                while (dReader.Read())
                {
                    namesCollection.Add(dReader["UserName"].ToString());
                }

            }
            else
            {
                MessageBox.Show("Data not found");
            }
            dReader.Close();

            comboBox1.AutoCompleteMode = AutoCompleteMode.Suggest;
            comboBox1.AutoCompleteSource = AutoCompleteSource.CustomSource;
            comboBox1.AutoCompleteCustomSource = namesCollection;

            textbox1.AutoCompleteMode = AutoCompleteMode.Suggest;
            textbox1.AutoCompleteSource = AutoCompleteSource.CustomSource;
            textbox1.AutoCompleteCustomSource = namesCollection;